Cationic copolymers which are insoluble in water, new dispensions and their use in the coating of papers

ABSTRACT

Cationic copolymers which are insoluble in water based on acrylamide, and a cationic monomer of general formula (I) ##STR1## in which R and R 1 , identical or different, represent a hydrogen atom or a methyl group, X represents an oxygen atom or an NH radical and n represents 2 or 3, containing in molar proportions 5 to 30% of cation units and cross-linked with 0.01% to 0.4% in molar proportions relative to the previous monomers of bisacrylamidoacetic acid and with about 0.01% to 0.1% in molar proportions relative to the monomers of bisacrylamidoacetic acid, self-reversible dispersions containing them and use in coating in the paper industry.

The present invention relates to new cationic copolymers which areinsoluble in water, new dispersions and their use in the coating ofpapers.

Cationic copolymers which are insoluble in water are described in theliterature and in particular cross-linked copolymers based on acrylamideand dialkylaminoalkyl (meth)acrylate with 5 to 100 ppm relative to theweight of monomers employed which have thickening properties for certainhousehold detergents and/or softeners (European Patent Application No.422179).

In the paper industry, for certain uses, notably graphics and morenotably for printing by photo-engraving, offset and flexographicprocesses, products are being sought which improve the smoothness of thepaper whilst controlling its microporosity and its affinity for inks(with an organic solvent or with water) in order to achieve an optimumprinting rendition (with regard to density, gloss, tint, smudging orstrike-through). These products must not modify other importantproperties such as opacity, whiteness, water resistance.

It would be desirable to have available products which are compatiblewith a large number of coating colours. In order to resolve thisproblem, new cationic copolymers have now been discovered which areinsoluble in water characterized by the fact that they are based onacrylamide, hereafter designated AAM, and a cationic monomer of generalformula (I) ##STR2## in which R and R₁ identical different representhydrogen atom or a methyl group, X represents an oxygen atom or an NHradical and n represents 2 or 3, containing in molar proportions 5 to30% of cation units and cross-linked with 0.01% to 0.4% in molarproportions relative to the aforementioned monomers ofbisacrylamidoacetic acid, hereafter designated ABAA.

In particular a subject of the invention is the copolymers describedabove, characterized in that the said copolymers are cross-linked withabout 0.01% to 0.1% in molar proportions relative to the monomers ofABAA.

More particularly a subject of the invention is the copolymers asdefined above in which the monomer of general formula (I) is eitherdimethylaminoethyl acrylate salified with hydrochloric acid, hereafterdesignated CHA, or dimethylaminoethyl acrylate quaternized with methylchloride, hereafter designated CMA, or diethylaminoethyl acrylatequaternized with methyl chloride, hereafter designated CME, ordimethylaminoethyl methacrylate quaternized with methyl chloride,hereafter designated CMM or finallymethacrylamidopropyltrimethylammonium chloride, hereafter designatedMAPTAC.

Advantageously, the cationic monomer is CMA. Among the copolymers basedon CMA, in particular a subject of the present invention is thosecontaining an AAM-CMA copolymer, with about 80-20 in molar proportions(namely, in particular 15 to 25 parts and more particularly 18 to 22parts of CMA for 85 to 75, in particular 82 to 78 parts of AAM),preferably cross-linked with about 0.02% mole of ABAA (namely inparticular from 0.015 to 0.025% mole ABAA).

The cationic copolymers defined above are insoluble in water but theyare swellable with water. Due to this fact they are capable of easilyabsorbing several times their own weight of water and of releasing itjust as easily when they are subjected, for example, to a strongshearing action or to drying.

Also a subject of the present invention is the compositions intended forthe coating of paper containing, as active ingredient, one of thepolymers defined previously.

These compositions are characterized by the fact that they areself-reversible dispersions, the average particle size of which is lessthan 20 μm, constituted hand by an aqueous phase, containing one of thepolymers defined previously, dispersed in an oil phase, and by at leasttwo emulsifying agents having an overall HLB value greater than 8 and ofwhich at least one of these emulsifying agents has an HLB value of lessthan 5.

The oil phase of the dispersion is constituted for example by one ormore hydrophobic hydrocarbons such as hexane, cyclohexane, straight orbranched chain C₈ -C₁₃ mineral oil cuts such as paraffin orparaffin/naphthenic oils in particular as regards commercial oils, thosesold under the name Shell white mineral oil, Isopar®, Solpar® orExxsol®.

The dispersed aqueous phase preferably represents 30 to 75% of the totalweight of the dispersion and it contains in suspension notably 20 to 45%by weight of a copolymer defined previously.

The emulsifying agent of HLB value of less than 5 is chosen from knownemulsifying agents, which are soluble in oils, such as sorbitanmonostearate, monooleate or sesquioleate, and it is advantageouslycontained in the dispersion in proportions of 2 to 8% by weight relativeto the total weight of the dispersed aqueous phase.

The emulsifying agents present in the dispersion must have an overallHLB value greater than 8, therefore it is usually necessary to employone or two emulsifying agents having an HLB value greater than 10, so asto compensate for the HLB value of less than 5 of at least one of theemulsifying agents. These emulsifying agents with an HLB value ofgreater than 10 are chosen from known hydrosoluble emulsifying agents,such as ethoxylated alkylphenols, sodium dialkylsulphosuccinates, soapsderived from C₁₀ -C₂₂ fatty acids.

The copolymers defined previously and the aforementioned compositionscontaining them, which were unknown, can be prepared by methods whichare similar to those described for the preparation of polymers and theknown compositions containing them.

The copolymers defined previously and the aforementioned compositionscan be prepared notably by radical-like polymerization in a water-in-oilemulsion. This type of polymerization is extensively described in theliterature and it consists of preparing, in the presence of one or moreemulsifiers soluble in oils, a water-in-oil emulsion the particle sizeof which is less than 20 μm and containing monomers in solution in thedispersed aqueous phase, then after careful deoxygenation of thisemulsion, carrying out the polymerization reaction with an initiatorusing one or more free radical generators, then finally cooling down thedispersion obtained to ambient temperature after having introduced intoit a sufficient quantity of hydrophilic surfactant(s), in order to makeit self-reversible.

The starting water-in-oil emulsion is prepared using water-in-oilemulsifying agents known for this purpose such as sorbitan monostearate,monooleate, or sesquioleate. These emulsifying agents must have an HLBvalue of less than 5 and they are advantageously contained in theemulsion in proportions of 2 to 8% by weight relative to the totalweight of the aqueous phase.

The oil phase of the emulsion is constituted for example by one or morehydrophobic hydrocarbons such as hexane, cyclohexane, straight orbranched chain C₈ -C₁₃ mineral oil cuts such as paraffin oils orparaffin/naphthenic oils marketed under the name of Shell white mineraloil, Isopar®, Solparx® or Exxsol®.

The dispersed aqueous phase represents about 30 to 75% of the totalweight of the emulsion and it contains in solution notably 20 to 45% byweight of monomers.

The polymerization reaction is initiated by one or more free radicalgenerating agents such as redox pairs, such as the cumenehydroperoxide-sodium bisulphite pair, azoic compounds such as azo-bis4,4' (cyano-4 pentanoic) acid, azo-bis amidinopropane hydrochloride.

The polymerization temperature depends on the polymerization initiatorchosen and can vary within limits ranging from 5° C. to 100° C. forexample, but in general the polymerization is carried out at normalpressure at temperatures of 10 to 80° C. Advantageously thepolymerization is carried out in a quasi adiabatic manner, at ambientpressure.

At the end of polymerization, one or more emulsifying agents, the HLBvalue of which is generally greater than 10, are introduced into thedispersion obtained. They are essentially hydrophilic products such asethoxylated alkylphenols, sodium dialkylsulphosuccinates, soaps derivingfrom C₁₀ -C₂₂ fatty acids. Advantageously, ethoxylated nonylphenols with6 to 12 moles of ethylene oxide are used. 1.5 to 8% by weight relativeto the total Weight of the dispersion of one or more emulsifying agentsare incorporated in the final dispersion, having an HLB value greaterthan 10 so that the overall HLB value of the emulsifying agents presentin the dispersion is greater than 8.

The copolymers according to the present invention may be easily isolatedfrom the dispersions containing them. For example, to do this thedispersion is diluted with the solvent used to prepare said copolymerssuch as cyclohexane or hexane, preferably one part by weight, thenintroduced slowly under agitation into 70 to 80 parts by weight ofanother solvent such as anhydrous acetone. After 30 minutes ofagitation, the precipitate obtained is filtered, then washed in thelatter solvent and finally dried under reduced pressure to a constantweight. In this way a quasi quantitative yield of a copolymer accordingto the invention is obtained in a solid state, in the form ofmicropearls which are insoluble in water.

The copolymers according to the present invention in particular whenthey are contained in a composition as described previously haveexcellent properties for conferring excellent smoothness to paper and/orcardboard supports.

For this use, the products according to the present invention areimplemented very simply with standard coating devices such as thoseknown under the names of "size-press", "size-tub", "calender sizing",etc., incorporating in the coating colour containing normal pigments andbinders as well as optionally other standard additives, the necessaryquantity of copolymer defined previously, in order to obtain the desiredsmoothness.

The copolymer is used in the form of the previously defined composition.As soon as it is incorporated in the aqueous coating colour containingthe normal ingredients such as pigments, binders, at a dose of drymatter comprised between about 50 and 75% by weight, the compositioncontaining the polymer defined previously reverses itself immediatelywhile releasing into the coating colour the copolymer swollen with waterbut insoluble in water. The doses used expressed in grams of drycopolymer relative to the weight of dry paper support vary from 0.05 to0.5%.

The copolymers and the compositions containing them according to thepresent invention permit the state of the surface of the paper supportsobtained both with a chemical pulp (pulp without wood) and with amechanical pulp (pulp with wood) to be considerably improved. Inaddition to improving the state of the surface and decreasing theroughness of the paper, particularly for papers derived from amechanical pulp, the products according to the invention also permit theconditions for implementing coating to be improved, notably:

by suppressing strike-through of the paper by the coating colour with asa result the elimination of the bleaching of the backing-roll,

by lubricating the blade: the machinability is improved with reducedrisks of breakdown;

by improving the dynamic water retention on the coated paper: the waterpenetrates into the support more slowly than in standard processes,which brings about a more even coating, without mask or running,

by providing coating colours that are compatible with products having acationic character.

It has been noted that the improvement of the smoothness of a papersupport was notably a function of the cross-linking rate of thecopolymer used, therefore of the cross-linking agent. For a proportionof cross-linking agent of less than 0.01% molar relative to the monomersof bisacrylamidoacetic acid practically no improvement in the smoothnessis obtained. Also starting with a proportion of cross-linking agent ofgreater than 0.4% molar of bisacrylamidoacetic acid, no furtherimprovement in the smoothness is observed.

The following examples illustrate the present invention without howeverlimiting it.

EXAMPLE 1

300 q of double distilled water, 6 q (28.5 mmole) of citric acidcrystallized with one molecule of water, 0.5 g of a 40% by weightaqueous solution of the sodium salt of diethylene triaminopentaaceticacid, designated DTPANa, 160 g of a commercial aqueous solution with 76%by weight of CMA, that being 0.63 mole, 178.5 g (2.51 mole) ofcrystallized acrylamide, 0.124 (0.63 mmole) of ABAA dissolvedextemporaneously in about 0.7 g of lN soda and 45 mg ofazobisacrylamidinopropane hydrochloride, currently designated ABAH,dissolved in the minimum amount of 0.lN soda are mixed together underagitation at ambient temperature. The total weight of this aqueoussolution is then adjusted to 700 g with double distilled water and itspH is adjusted, if necessary, to 3.5 with a few drops of an aqueoussolution of hydrochloric acid. An aqueous solution is obtaineddesignated S.

Furthermore, 241 g of commercial paraffin-naphthenic oil having aboiling point of 300 to 350° C, hereafter designated H, and 21 g ofsorbitan sesquioleate are mixed together under agitation at ambienttemperature. Then the aforementioned aqueous solution S is introducedinto this mixture over about 15 minutes under strong agitation whilemaintaining the temperature around +5° C. The dispersion obtained issubjected for about 1 minute to vigorous agitation with an Ultra-Turaxtype turbine so as to obtain a Brookfield viscosity of about 3700 mPa.sdetermined at 20° C. with a Brookfield RVT apparatus.

The emulsion thus obtained is transferred into a polymerization reactor,then it is carefully deoxygenated by bubbling nitrogen through it whilemaintaining the temperature below 10° C. Then, under agitation, 5 ml ofa solution of 10 g of cumene hydroperoxide in one liter of theaforementioned oil H is introduced over 5 minutes, then 23 ml of asolution of 2.24 g of sodium metabisulphite in one liter of doubledistilled water is introduced over 25 minutes. The whole is left toallow the polymerization reaction to develop in a quasi adiabaticmanner. Over about 25 minutes the reaction medium temperature increases62° C., with an average gradient of 2 to 3° C. per minute. When thetemperature of the reaction medium decreases it is heated and is kept at80° C. under agitation for one hour, then it is cooled down to 50° C. Atthis temperature 10 g of nonylphenol ethoxylated with 10 moles ofethylene oxide and 10 g of nonylphenol ethoxylated with 12 moles ofethylene oxide are introduced then the reaction medium is cooled down toambient temperature.

In this way about 1 kg of a water-in-oil emulsion is obtained containingin the dispersed aqueous phase a copolymer AAM-CMA, 80-20 in molarproportions, cross-linked with 0.02% in molar proportions of ABAArelative to the monomers used. The emulsion has a Brookfield viscosityof 710 mPa.s. determined at 20° C. and the isolated copolymer insuspension at 1% by weight in water has a Brookfield viscosity of 27400mPa.s. and at 1% by weight in a 0.1% aqueous solution of sodium chloridea Brookfield viscosity of1280 mPa.s.

EXAMPLE 2

Example 1 is reproduced using only 62 mg (0.315 mmole) of ABAA. In thisway about 1 kg of a water-in-oil emulsion is obtained containing in thedispersed aqueous phase a copolymer AAM-CMA, 80-20 in molar proportions,cross-linked with 0.01% in molar proportions relative to the ABAAmonomers used. The emulsion has a Brookfield viscosity of 1040 mPa.sdetermined at 20° C. and the isolated copolymer in suspension at 1% byweight in water has a Brookfield viscosity of 15900 mPa.s and at 1% byweight in a 0.1% aqueous solution of sodium chloride a Brookfieldviscosity of 200 mPa.s.

EXAMPLES A1-A3 AND COMPARISON EXAMPLES C1-C3

In these examples, a paper support obtained, either with a chemicalpulp, Bl, or a mechanical pulp, B2, or a non-sized wood pulp, B3, istreated with a coating color the composition of which in dry material,expressed in g, is given in Table I, on a Helicoater MK IV type from theCharlestown Engineering Company. The weight of the deposit, as well asthe pH and the viscosity of the coating colour are also mentioned inTable I. The coated paper is then subjected to drying under infrared at36 Kwh of power for 120 seconds, then its smoothness is determined witha BEKK measuring device according to French Standard NF Q 03-012 ofFebruary 1974 and the results are expressed in seconds. The smoothnessis better the longer the time.

The BEKK porosity which determines the permeability to air of a paper ismeasured with the same device which allows the BEKK smoothness to beknown by replacing the flat die with a die carrying concentric grooves.With this device, the time required for 100 cm³ of air to cross 1 cm² ofsample under a low pressure of 380 mbar is determined, and the result isexpressed in seconds. In order to improve the accuracy of thismeasurement, measurements are taken on several identical superimposedsamples and the result is expressed by dividing the measured time by thenumber of samples.

In Table I, the weights are expressed in grams and the viscosities,determined on a Brookfield RVT apparatus at 20° C, at the speed and withthe axis recommended for the value indicated, are expressed in mPa.s.The rheology modifiers of the coating colour are either the productsdescribed in the examples, or carboxymethylcellulose, designated CMC,marketed by the Assignee under the reference TYLOSE® VCLL, and which iscurrently the most used rheology modifier. The binder Ll is a bindercurrently used in paper coating and it is a latex SBR marketed by theCompany Dow France under the reference DL 675 SBR. The pH of the coatingcolour is adjusted to the value indicated with 10% soda. The angle ofthe blade of the coating apparatus is expressed in degrees.

The viscosity and the pH of the coating colors of these two examples arestable over time and they have no applicability problems: the bladepressures used are approximately the same.

From examination of Table I it can be noted that by using kaolin as thepigment, the composition according to the present invention gives a BEKKsmoothness 76% greater than that given by CMC. Consequently this gainallows a saving of deposit of at least 1 g/m², i.e. a saving of 17%.Similarly, TABER test, standard TAPPI T 476 pm76, which determines theresistance of the paper to moist abrasion, it is noted that the productaccording to the invention gives an average turbidity value expressed inNtu of 153 against 178 for the CMC, which shows that the compositionaccording to the present invention gives the treated paper betterresistance to dampness.

With the use of calcium carbonate as the pigment, the compositionaccording to the present invention considerably improves the smoothness(-95%) and the porosity (-33%). In addition, the composition of thepresent invention was tested in a Heliotest which allows the behavior ofpapers during printing with photo-engraving to be simulated with a highdegree of precision.

With the formulations given in Examples A3 and C3 (cf. Table I) and witha deposit of 8.6 to 8.9 g/m² the distance to the twentieth missing pointmoves from 3 mm (Example C3) to 30 mm (Example A3) which constitutes aremarkable performance.

The Heliotest consists of carrying out printing of a calendered paperwith a copper cylinder the surface of which is engraved with square orround cells. The depth of the cells is greater (a maximum of 3 to 4tenths of a millimeter) the darker the chosen printing is. The lowerpart of the cylinder bathes in the ink, the excess ink entrained is theneliminated with a bevelled scraper and finally the cylinder transfersthe residual ink to the paper under high pressure applied using a rubbercylinder pressing the paper onto the engraved copper cylinder. The testis carried out at a constant speed of 1 m/s on a calendered paper. Theresults are expressed by determining the distance to the twentiethmissing point using a given quantity of ink (3 to 4 drops only).

                                      TABLE I                                     __________________________________________________________________________                       Ex C1                                                                             EX A1                                                                             EX C2                                                                             EX A2                                                                             EX C3                                                                             EX A3                                  __________________________________________________________________________    Formulation of the                                                            coating mass                                                                  Pigment            0   0   100 100 100 100                                    calcium carbonate                                                             kaolin             100 100 0   0   0   0                                      talc               0   0   0                                                  Binder                                                                        nature             L1  L1  L1  L1  L1  L1                                     weight             12  12  12  12  12  12                                     Rheology modifier                                                             nature             CMC EX 1                                                                              CMC EX 2                                                                              CMC Ex 1                                   weight expressed   1   1.3 1   0.7 1   1.7                                    in dry state                                                                  Dry extract                                                                              in % by weight                                                                        59.0                                                                              59.0                                                                              61.5                                                                              61.5                                                                              61.5                                                                              61.5                                   viscosity  mPa.s   390 1210                                                   pH                 8   8   9   9   9   9                                      Support                                                                       nature             B3  B3  B3  B3  B3  B3                                     basis weight g/m.sup.2                                                                           39  39  39  39  39  39                                     Operating conditions                                                          speed      m/min   600 600 600 600 600 600                                    angle of the blade                                                                       in degrees                                                                            59  59  59  59  59  59                                     thickness of blade                                                                       mm      0.508                                                                             0.508                                                                             0.508                                                                             0.508                                                                             0.508                                                                             0.508                                  Results                                                                       deposit    g/m.sup.2                                                                             8   8   8   8   8   8                                      BEKK smoothness                                                                          seconds 44.0                                                                              57.2                                                                              30.8                                                                              73.7                                                                              27  52.5                                   BEKK porosity                                                                            seconds 42  29  21  14  27.9                                                                              18.4                                   TABER turbidity                                                                          Ntu     32  9   102 294 105 159                                    Deposit    g/m.sup.2                                                                             8   8   8   8   8   8                                      __________________________________________________________________________

What is claimed is:
 1. A self-reversible dispersion the average particlesize of which is less than 20 μm, comprising an aqueous phase dispersedin an oil phase and at least two emulsifying agents having an overallHLB value greater than 8 and of which at least one of these agents hasan HLB value of less than 5, wherein said dispersion contains in theaqueous phase at least one water-insoluble and water-swellable cationiccopolymer of the formula ##STR3## in which R and R₁, identical ordifferent, represent a hydrogen atom or a methyl group, X represents anoxygen atom or an NH radical and n represents the number 2 or 3,containing in molar proportions 5 to 30% of cation units andcross-linked with 0.01% to 0.4%, in molar proportions relative to saidmonomers, of bisacrylamidoacetic acid.
 2. Dispersion according to claim1, wherein said dispersion contains by weight in suspension in thedispersed aqueous phase from 20 to 45% of said cationic copolymer. 3.Dispersion according to claim 2, wherein the dispersed aqueous phaserepresents 30 to 75% of the total weight of the dispersion, and thequantity of bisacrylamidoacetic acid used to cross-link said monomers is0.01% to 0.1% in molar proportions.
 4. Dispersion according to claim 3,obtained by a process consisting of preparing, in the presence of one ormore emulsifying agents soluble in oils, a water-in-oil emulsion theparticles of which have a size of less than 20 μm and containingmonomers in solution in the dispersed aqueous phase, then after carefuldeoxygenation of this emulsion, of carrying out the polymerizationreaction with an initiator comprising one or more free radicalgenerators, then finally of cooling down the dispersion obtained toambient temperature after having introduced into it a sufficientquantity of emulsifying agents to render it self-reversible. 5.Dispersion according to claim 2, obtained by a process consisting ofpreparing, in the presence of one or more emulsifying agents soluble inoils, a water-in-oil emulsion the particles of which have a size of lessthan 20 μm and containing monomers in solution in the dispersed aqueousphase, then after careful deoxygenation of this emulsion, of carryingout the polymerization reaction with an initiator comprising one or morefree radical generators, then finally of cooling down the dispersionobtained to ambient temperature after having introduced into it asufficient quantity of emulsifying agents to render it self-reversible.6. Dispersion according to claim 1 wherein the dispersed aqueous phaserepresents 30 to 75% of the total weight of the dispersion. 7.Dispersion according to claim 6, obtained by a process consisting ofpreparing, in the presence of one or more emulsifying agents soluble inoils, a water-in-oil emulsion the particles of which have a size of lessthan 20 μm and containing monomers in solution in the dispersed aqueousphase, then after careful deoxygenation of this emulsion, of carryingout the polymerization reaction with an initiator comprising one or morefree radicals generators, then finally of cooling down the dispersionobtained to ambient temperature after having introduced into it asufficient quantity of emulsifying agents to render it self-reversible.8. Dispersion according to claim 1 that is obtained by a processconsisting of preparing, in the presence of one or more emulsifyingagents soluble in oils, a water-in-oil emulsion the particles of whichhave a size of less than 20 μm and containing monomers in solution inthe dispersed aqueous phase, then after careful deoxygenation of thisemulsion, of carrying out the polymerization reaction with an initiatorcomprising one or more free radical generators, then finally of coolingdown the dispersion obtained to ambient temperature after havingintroduced into it a sufficient quantity of emulsifying agents to renderit self-reversible.